1. Field of the Invention
This invention relates to a method of encapsulating a part of a substrate, especially the splice area of a telephone cable.
2. Summary of the Prior Art
It is common practice to provide a waterproof encapsulation around a part of a substrate by means of a sealing material which flows around the substrate during the encapsulation process, but is relatively viscous in the final product. Since the sealant must be sufficiently liquid to flow around the substrate, it must be confined by a closure member, which is frequently heat-shrinkable. In many cases, the encapsulation process requires the use of heat to change the viscosity of the sealing material, for example by melting a fusible solid so that it can flow into sealing contact with the substrate or by curing a two-part liquid curing system. Two methods have been used or proposed for use to supply such heat to the sealing material. The first, which is widely used in practice, is to heat the whole assembly externally so that the sealing material is heated by a combination of convection and conduction. The second, which is described in U.S. Pat. No. 3,396,455, makes use of infra-red radiation in combination with a heat-shrinkable sleeve as the closure member, the sleeve absorbing part of the radiation so that it is heated to its shrinkage temperature, but transmitting sufficient of the radiation to fuse an infra-red absorptive insert within the sleeve. A disadvantage of both these methods is that when extended heating is required, for example in order to melt a large quantity of sealant when encapsulating a telephone cable splice, it is difficult to avoid damaging one or more of the components of the assembly, because the exterior of the assembly reaches a much higher temperature than the interior. This problem is particular apparent when encapsulating a splice comprising a cable having a thermoplastic insulating jacket, e.g. of polyethylene or another polyolefin.